Deep frying – How does it cook?
Deep frying is a cooking method in which food is submerged in hot fat e.g. oil. This is normally performed with a deep fryer or chip pan; industrially, a pressure fryer or vacuum fryer may be used.
Deep frying is classified as a dry cooking method because no water is used. Due to the high temperature involved and the high heat conduction of oil, it cooks food extremely quickly.
Proper Technique for deep frying foods
If performed properly, deep-frying does not make food excessively greasy, because the moisture in the food repels the oil. The hot oil heats the water within the food, steaming it; oil cannot go against the direction of this powerful flow because (due to its high temperature) the water vapor pushes the bubbles toward the surface. As long as the oil is hot enough and the food is not immersed in the oil for too long, oil penetration will be confined to the outer surface. However, if the food is cooked in the oil for too long, much of the water will be lost and the oil will begin to penetrate the food. The correct frying temperature depends on the thickness and type of food, but in most cases it lies between 347–374 °F.
How to tell if your cooking oil needs to be changed
Overheating or over-using the frying oil leads to formation of rancid-tasting products of oxidation, polymerization, and other deleterious, unintended or even toxic compounds such as acrylamide (from starchy foods
Some useful tests and indicators of excessive oil deterioration are the following:
Sensory: Darkening, smoke, foaming, thickening, rancid taste and unpleasant smell when heating.